That tell tale sound...

[Irode]

In many games their are many monsters, sometimes you need to be able to prepare for these and such. This is why in many games certain monsters have noises that they each make to signal that they are behind about to surprise anal rape with their scary claws you or round the next corner.

These are used in many many genres that include such baddies, my question is what is your favorite warning from a game from an enemy?
The reasons behind it may be the actual monster, hearing it and then feeling the "oh fuck" emotion ring in your head as you realise your about to again be anal raped.

Anyway, mine would be the boomer from left 4 dead, he just sounds so sickly that you know its him and he wants to bring his pain to you. He's fat, he's disgusting and he's kinda cute, he's a damn good monster. (or infected, whatever)

Hmm, seems like a good first thread.

 

[Engarde]

Regenerators in Resident Evil 4. The breathing, and the shuffling....heheh.

 

[Omikron009]

I don't know about my favourite, but I do know my least favourites:

1. Mudcrabs in Oblivion. That scratching skittering noise just bothers me, as well as the combat music that won't go away until you find and kill the little bastard.

2. Skeletons in Dragon Age. That sickly groaning noise is awful.

 

[silver wolf009]

"Emergency security procedures initiated, use of lethal force authorized. Threat level omega, weapons free." Sentry bots in fallout 3 before they open fire with gatling cannons.

That horrible screaming noise that big dadies let off accompanied by that "Dont let em get me MR. B!" when your shadow hits the little sister.

Again from bioshock. "My rose! GIVE IT BACK GIVE IT BACK GIVE IT BACK!!!!!!!!!"

"By the gods, ASSAULT, ASSALUT"

 

[Carbonic Penguin]

I always liked hearing the tank's breathing (left 4 dead) before you encounter it. Without the captions. I always go 'what's tha.... oooohh... tank ahead guys... gaah'. And what else...? I can't think of anything atm...

 

[Furious Styles]

Zombies in oblivion, that groaning noise still makes me freeze.

 

[Jezzascmezza]

The witches from Left 4 Dead.
The creepy music and their shrieks haunt my dreams...

 

[Funkiest Monkey]

Alright, lets go on. Wait. Wait. Is that...? Oh fuck. Oh fuck me. Shit! Turn off your light. Turn it off! Okay, don't make a noise. Don't even walk quickly. FUCK. Don't even move at all! OHSHITWHOTHEFUCKSHOTTHECAR?! NOOOOOOO!

 

[Extraintrovert]

The Silent Hill series' radio static.

Oh sweet merciful crap, this.

In the interest of not being completely unoriginal however, I also recommend the zombies in Half-Life 2 and its Episodes. The moaning of the standard ones, the laboured breathing of the poison ones, the crackling static of the Combine ones, and of course the howling, snarling and screaming of the fast ones. Perfect mixture of a warning and an exercise in spontaneous defecation.

 

[Celtic_Kerr]

I have to emulate the bioshock post really. I once walked past a Little Sister without knowing I was walking past a little sister, and set us off...

the next ten second are spent thinking "SHIT! Groaning sound, where the hell is he?!"

 

[Harlemura]

I'm usually on bad terms with the little "beepbeep" sound of a Team Fortress 2 Demoman detonating his sticky bombs.
If that sound directly follows me going through a door, I spend the split second before being blown to smitheroons bracing myself for that smarmy grin that's going to follow on the freezecam.
I hate Demomen sometimes...
EDIT:
After reading the OP properly, I noticed that may not count as the Demoman isn't really a creature... well, you could argue he is, but whatever.

I'd probably have to second the Regenerators from Resident Evil 4. If I hear anything that sounds even remotely like that breathing, I get shudders.

 

[VJZ4life]

The sound of one of those cockroach creatures in RE:5 mercenaries mode.
My friend and i would run around like madmen after hearing that hissing/clicking sound. Only to get skewered by it's spear like legs seconds after

 

[GundamSentinel]

Those screeching poison headcrabs in Half-Life 2. Those were so scary, not to mention the moaning poison zombies.

 

[Voodoomancer]

Alright, lets go on. Wait. Wait. Is that...? Oh fuck. Oh fuck me. Shit! Turn off your light. Turn it off! Okay, don't make a noise. Don't even walk quickly. FUCK. Don't even move at all! OHSHITWHOTHEFUCKSHOTTHECAR?! NOOOOOOO!

DAMMIT, ELLIS, YOU SHOT THE DAMN CAR, YOU ST... *gets throatcut by mad witch*

Also, poison headcrabs in HL2, Not too scary, but sure are creepy.

 

[Irode]

I'm usually on bad terms with the little "beepbeep" sound of a Team Fortress 2 Demoman detonating his sticky bombs.
If that sound directly follows me going through a door, I spend the split second before being blown to smitheroons bracing myself for that smarmy grin that's going to follow on the freezecam.
I hate Demomen sometimes...
EDIT:
After reading the OP properly, I noticed that may not count as the Demoman isn't really a creature... well, you could argue he is, but whatever.

I'd probably have to second the Regenerators from Resident Evil 4. If I hear anything that sounds even remotely like that breathing, I get shudders.

Nah it doesn't matter to me!
I generally meant enemies, monsters just seemed to work better as a theme.

 

[Axolotl]

The screech of cliffracers still haunts my nightmares.

 

[Subzerowings]

The sound of dying insects in Fallout 3.
It made me not kill radroaches or bloatflies.

EDIT: Oh, scary noises.
Erm...
Not really scary, but you know you're fucked when you hear those invisible chimaera in Resistance 2.

 

[T-Bone24]

The screaming of the ReDeads in Wind Waker, especially. Going from 0 to Pantsshit in 3 seconds.